Models and tools
Models do the reasoning. Sonnet handles most coding tasks well; Opus provides stronger reasoning for complex architectural decisions. Switch with /model during a session or start with claude --model <name>.
Tools are what make Claude Code agentic. Without tools, Claude can only respond with text. With tools, it can act. The built-in tools fall into five categories:
| Category | What Claude can do |
|---|---|
| File operations | Read files, edit code, create files, rename and reorganize |
| Search | Find files by pattern, search content with regex, explore codebases |
| Execution | Run shell commands, start servers, run tests, use git |
| Web | Search the web, fetch documentation, look up error messages |
| Code intelligence | See type errors after edits, jump to definitions, find references (via plugins) |
Claude chooses which tools to use based on your prompt and what it learns along the way. Each tool use returns information that feeds back into the loop. Beyond these, Claude has tools for spawning subagents, asking you questions, and orchestration.
Check your understanding
Section titled “Check your understanding”Question 1Which is NOT one of the five built-in tool categories?
The five categories are file operations, search, execution, web, and code intelligence. Databases are reached via MCP.
Question 2When should you reach for Opus over Sonnet?
Sonnet handles most coding tasks; Opus is for complex reasoning.